The elucidation of changes in populations of immunoglobulin-secreting cells has been a cumbersome process. We present a simplified method for the enumeration of human immunoglobulin-secreting cells with an ELISA spot assay (ESA). This method is specific, will detect all isotypes, including IgE, and is sensitive, detecting as little as 10 pg of antibody secreted. In this article, we describe the methodology for performing the ESA, demonstrate the kinetics for optimal use in both B-lymphoblastoid lines and fresh B cells, and determine the correlation between the ESA and immunoglobulin secretion under various experimental conditions. This assay permits an estimate of the level of immunoglobulin secreted per cell, thus distinguishing expansion of immunoglobulin-secreting cell populations from increases in average (per cell) immunoglobulin production. The combination of ESA and quantitation of immunoglobulin in supernatants of cultured cells provides an easy and reliable means for studying the regulation of immunoglobulin secretion.